JPH07152008A - Measuring method of magnetic field and magneto-optical sensor using that - Google Patents

Abstract

PURPOSE:To obtain a measuring method of a magnetic field of high intensity using RIG which is inexpensive and of high massproductivity, as a magneto- optical material, and to obtain a magneto-optical sensor using this method. CONSTITUTION:The intensity of a magnetic field is measured by using rare earth iron garnet(RIG) as a magneto-optical material. In this method, a magnetic field controlling member 24 made a magnetic material is disposed near the rare earth iron garnet to control the substantial intensity of the magnetic field applied on the RIG to smaller than the saturation magnetic field of the RIG. By constituting the detecting part for a magnetic field of the detecting terminal 23 using the RIG film as a magneto-optical material and the magnetic field controlling member 24 made a magnetic material, even a magnetic field of high intensity which can not be measured with a magneto-optical sensor using a conventional RIG film as a magneto-optical material can be measured. By using the RIG film, improvement in the massproductivity and the cost reduction of the sensor can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a high magnetic field intensity using the Faraday effect of a rare earth iron garnet film,
The present invention relates to an optical magnetic field sensor utilizing this. In particular, the present invention relates to an optical magnetic field sensor that detects the magnitude of a current by measuring a high magnetic field strength generated around a high-voltage power transmission line such as a power transmission line that supplies power, a power receiving and transforming facility (hereinafter, cubicle), or a high-voltage wiring circuit.

[0002]

2. Description of the Related Art Electric power is transmitted from a power plant to a substation or from a substation to a substation via a high voltage power transmission line or a high voltage wiring circuit. A transformer-type current sensor has been used as a device for detecting an abnormality in the current flowing through the high-voltage power transmission line or the high-voltage wiring circuit, for example, an abnormality such as disconnection. This transformer-type current sensor has an iron core wound with an insulating wire in a coil shape, and has various problems such as large size, large weight, and poor insulation. In recent years, there are plans to replace the transformer type current sensor with an optical magnetic field sensor. This is because the optical magnetic field sensor can be made smaller and lighter and has excellent insulation properties.

FIG. 16 shows the basic structure of a current measuring optical magnetic field sensor used for this purpose. The light emitted from the light source 1 passes through the optical fiber 2, the lens 3, and the polarization beam splitter (hereinafter referred to as PBS) 4, becomes linearly polarized light, passes through the half-wave plate 5, and enters the magneto-optical material 6. Here, when the light passes through the magneto-optical material 6, the light is rotated according to the strength of the magnetic field to be measured (hereinafter referred to as the magnetic field), and passes through the PBS 7 to have the strength according to the strength of the magnetic field. It is focused on the fiber 9. Here, the half-wave plate 5 is used to rotate the polarization plane of the passing light of the PBS 4 by 45 degrees so that the relative polarization angle between the passing light and the PBS 7 is 45 degrees (when the magnetic field is 0), and the sensitivity of the sensor is maximum. This is because It should be noted that the half-wave plate 5 and the magneto-optical material 6 do not have a big problem in characteristics even if their positions are interchanged.

Now, I ₀ is the intensity of light incident on the magneto-optical material 6, I is the light intensity after passing through the PBS 7, Hs is the saturation magnetic field intensity of the magneto-optical material, θ is the Faraday rotation angle, and H is
Where (H = Hs in the case of H> Hs) is the strength of the magnetic field, the relationship between the intensity of the light after passing through the PBS 7 and the strength of the magnetic field is expressed by Equation 1. That is, the optical magnetic field sensor utilizes the relationship of the equation (1).

[0005]

## EQU1 ## I / I ₀ = cos ² (θ) + (H ² / Hs ² ) .sin ² (θ)

The optical magnetic field sensor is generally constructed by connecting a light source 1, a detecting section 10 and an output section 11 with optical fibers 2 and 9, respectively, as shown in FIG. Detector 1
0 is created by mounting the part surrounded by the broken line in FIG. 7 in a container made of a synthetic resin plate, for example. And the output unit 11
Is composed of a photodetector 12 and a signal processing circuit 13. In use, the detection end is installed so that the magnetic field and the path of light passing through the magneto-optical material 6 are parallel to each other.

By the way, in the high-voltage power receiving and transforming equipment, the electric current flowing in the electric wire is about 30,000 amperes, and the strength of the magnetic field generated near the electric wire is about 3,000 Oe.
Therefore, if an optical magnetic field sensor is used to measure the strength of this magnetic field, Hs is 3
Magneto-optical materials in excess of 000 Oe must be used. A magneto-optical material satisfying this is lead glass.

However, if the magneto-optical sensor is constructed by using lead glass, it is certainly suitable for detecting such a high magnetic field, but it is not suitable for mass production and θ is small.
There is a problem that the device cannot be downsized.

In order to reduce the size of the device, it is necessary to use a magneto-optical material having a large θ. Rare earth iron garnet (hereinafter referred to as “RIG”) is known as a magneto-optical material having a large θ, relatively inexpensive and good in mass productivity. Therefore, it has been attempted to use the optical magnetic field sensor using this RIG to detect the high-intensity magnetic field. However, this attempt has not always been successful. This is because the Hs of RIG depends on the composition but is at most 1500 Oe.

[0010]

The present invention has been made in consideration of the above situation. That is, an object of the present invention is to provide a method for measuring a high-strength magnetic field using an inexpensive and highly mass-producible RIG as a magneto-optical material, and an optical magnetic field sensor using the method.

[0011]

The measuring method of the present invention for solving the above-mentioned problems is a method of measuring the strength of a magnetic field using a rare earth iron garnet as a magneto-optical material. An adjusting member is provided to make the substantial strength of the magnetic field applied to the rare earth iron garnet less than the saturation magnetic field strength of the rare earth iron garnet, and the optical magnetic field sensor of the present invention that embodies this is a light source and a magnetic field measuring device. In an optical magnetic field sensor basically composed of a detection unit and an output unit, the magnetic measurement detection unit is composed of a detection terminal and a magnetic field adjusting member made of a magnetic material, and is a magnetic element which is an essential component of the detection terminal. The optical material uses rare earth iron garnet.

[0012]

The detection terminal used in the present invention may be constituted by a PBS, a half-wave plate, a rare earth iron garnet film, and a PBS which are generally used in this order. You may comprise only an iron garnet film | membrane. Importantly, the rare earth iron garnet film is always arranged in the magnetic field.

The detector of the optical magnetic field sensor of the present invention comprises a detection terminal and a magnetic field adjusting member made of a magnetic material. For example, when the magnetic field adjusting member has a structure covering the detection terminal, Be sure that a part of the detection terminal is exposed or the surface can be seen from the outside. Of course, a part of the container forming the detection terminal may be made of a magnetic material member, and this may be used as a magnetic field adjusting member.

By configuring the detector in this way,
When the detection unit is installed in the magnetic field, a reverse magnetic field is generated in the detection unit by the magnetic field adjustment member, and the magnetic field strength applied to the detection terminal is reduced. As a result, even if such a detector is installed in a magnetic field that greatly exceeds the saturation magnetic field strength Hs of the rare earth iron garnet, the magnetic field strength applied to the rare earth iron garnet in the detector can be less than the above Hs. . Therefore, a ferromagnetic material is selected as the magnetic material depending on the magnitude of the reverse magnetic field generated.

The magnetic field adjusting member may be of any shape as long as it can effectively generate a reverse magnetic field and reduce the magnetic field applied to the rare earth iron garnet.
Of course, the specifications of the magnetic field adjusting member are adjusted according to the magnitude of the reverse magnetic field generated.

As described above, according to the method and apparatus of the present invention, it is possible to measure a high magnetic field strength significantly exceeding Hs of rare earth iron garnet by using the rare earth iron garnet which is inexpensive and easy to mass produce.

[0017]

EXAMPLES The present invention will be described in more detail below with reference to examples. (Embodiment 1) FIGS. 1 and 2 show the structure of a detection unit 20 of an optical magnetic field sensor manufactured according to the present invention. 1 is a view of the detection unit 20 as seen from above, and FIG. 2 shows the same detection unit as the optical fiber 2
It is the figure seen from the 1 and 22 side, ie, the light entrance and exit side. The detection unit 20 has a width of 20 mm and a depth of 11 m, which is formed by forming a detection terminal 23 having a width of 16 mm, a depth of 7 mm, and a thickness of 8 from a pure iron plate having a thickness of 1 mm (hereinafter, simply referred to as “iron plate”).
It is provided inside the magnetic field adjusting member 24 of m × height 12 mm.

The main part of the detection terminal 23 is shown in FIG. That is, PBSs 25 and 26 are used as polarizers, and a rare earth iron garnet film (composition: about 25 μm thick) is used as a magneto-optical material.
(YbYb) ₅ Fe ₃ O ₁₂ Hereinafter referred to as “this RIG film”. ) 27, and these and the half-wave plate 28 are attached in the order of the PBS 25, the half-wave plate 28, the RIG film 27, and the PBS 26 in a container made of a synthetic resin plate to manufacture a detection terminal. In addition,
The PBSs 25 and 26 were placed on the same plane and a half-wave plate 28 was placed immediately in front of the main RIG film 27 so as to be placed at 45 degrees.

When using the detecting section 20 of this embodiment,
In FIG. 2, the detecting unit 20 and the magnetic field direction are arranged such that the A surface of the magnetic field adjusting member is in a direction in which the magnetic field decreases in the gradient vector direction defined by gradH with respect to the magnetic field H.
Was placed. Then, as a light source (not shown), a light emitting diode which emits light having a wavelength of 0.85 μm was used, and light was incident on the optical fiber 21 from the light source. This light is PBS
It is made into linearly polarized light by 25, and the main R is transmitted through the half-wave plate 28.
It is incident on the IG film 27. When the light passes through the RIG film 27, the light is rotated according to the strength of the magnetic field applied to the RIG film 27, and the polarization plane is rotated. After that, the light is PBS
By passing through 26, it is converted into a light quantity corresponding to the magnetic field strength. The light passing through the PBS 26 is the optical fiber 2
The light was incident on a photodetector (not shown) using a Si photodiode via 2 and was photoelectrically converted by the photodetector. The current signal thus obtained was input to a signal processing circuit (not shown). Then, the output signal from the signal processing circuit was voltage-converted and measured. Therefore, the measured value is a relative value. The detection unit of the optical magnetic field sensor of this example having the above-described configuration was installed in the magnetic field, and the relationship between the magnetic field strength and the output was obtained. The Hs of the RIG film used in this example was 1350 Oe at room temperature, and the magnetic field strength was changed within a range of ± 5000 Oe. The obtained results are shown in a1 of FIG.

As can be seen from FIG. 4, the magnetic field strength is ± 500.
Even in the range of 0 Oe, the linearity between the output of the optical magnetic field sensor and the magnetic field strength is maintained, and it can be seen that the optical magnetic field sensor of this embodiment is effective.

(Embodiment 2) The detection unit 20 and the magnetic field direction are shown in FIG. 2, and the surface A of the magnetic field adjusting member is gra against the magnetic field H.
The detection unit 20 was installed so that the magnetic field decreased in the direction of the gradient vector defined by dH. Then, other than that, the same apparatus as in Example 1 was used, and the relationship between the output of the optical magnetic field sensor and the magnetic field strength was similarly obtained. The obtained results are shown in a2 of FIG.

As can be seen from FIG. 4, the linearity between the output of the optical magnetic field sensor and the magnetic field strength is not lost even in the method of use of this embodiment. However, the inclination is gentler than that of a1, and it can be seen that a wider range of changes in magnetic field strength can be accommodated.

Further, the results of a1 and a2 in FIG. 4 indicate that when there are two electric wires or the like which are magnetic field generation sources, the optical magnetic field sensor of the present invention is used even in the central portion where the magnetic field strengths from both are equal. It can be said that this indicates that a stronger signal can be obtained from the source than the other.

(Examples 3 and 4) As shown in FIG. 5, the main parts of the detection terminal are a total reflection prism 31, a polarizer 32, a main RIG film 33, a polarizer 34, and a total reflection prism 35, which are arranged in this order. The same optical magnetic field sensor as in Examples 1 and 2 was assembled except that the above configuration was made, and the relationship between the output of the optical magnetic field sensor and the magnetic field strength was similarly obtained (Examples 3 and 4). As a result, as in Examples 1 and 2, respectively, a good proportional relationship was found between the output of the optical magnetic field sensor and the magnetic field strength in the range of ± 5000 Oe.

(Examples 5 to 14) The structure of the magnetic field adjusting member is a plate (FIG. 6, Example 5), an open U-shape (FIG. 7, Example 6), and One in which a plate-shaped iron plate is provided on the back surface of the magnetic field adjusting member of Example 1 (FIG. 8, Example 7), and one in which iron plates are attached in opposite directions to both ends of the U-shaped magnetic field adjusting member ( FIG. 9, Example 8), a rectangular tube (FIG. 10, Example 9), four iron plates attached to the side surface of one iron plate (FIG. 11,
Example 10), a tubular shape (FIG. 12, Example 1)
1), a spherical shape having an opening (FIG. 13, Example 12), a circular tube with a part cut away and an iron plate attached (FIG. 14, Example 13), and an iron plate formed into an Ω shape. An optical magnetic field sensor similar to that of Example 1 was assembled except that a bent product (FIG. 15, Example 14) was used, and the relationship between the output of the optical magnetic field sensor and the magnetic field strength was obtained in the same manner as in Example 1. . As a result, as in Example 1, a good proportional relationship was observed between the output of the optical magnetic field sensor and the magnetic field strength in the range of ± 5000 Oe.

(Embodiment 15) Of the six faces of the container constituting the detection terminal, one face and three faces on both sides thereof are made of iron plate and the other are made of synthetic resin plate. An optical magnetic field sensor similar to that of the first embodiment is assembled except that a member having a member such as a magneto-optical element constituting the above is used as the detecting unit, and the relationship between the output of the optical magnetic field sensor and the magnetic field strength is similar to the first embodiment. I asked. As a result, ± 5000 as in Example 1.
In the range of Oe, a good proportional relationship was found between the output of the optical magnetic field sensor and the magnetic field strength.

(Examples 16 and 17) Similar to the conventional product shown in FIG. 16, the essential parts of the detection terminal are the optical fiber, lens, PBS, and
Half-wave plate, RIG film, PBS, lens, optical fiber,
Optical magnetic field sensors similar to those in Examples 1 and 2 were assembled except that they were arranged in this order, and the relationship between the output of the optical magnetic field sensor and the magnetic field strength was similarly obtained (Examples 6 and 7). As a result, as in Examples 1 and 2, respectively, a good proportional relationship was found between the output of the optical magnetic field sensor and the magnetic field strength in the range of ± 5000 Oe.

(Prior art example) The magnetic field adjusting member of the detecting portion of the optical magnetic field sensor of the first embodiment was removed, and the relationship between the optical magnetic field sensor output and the magnetic field strength was obtained in the same manner as in the first embodiment.
The obtained result is shown in b of FIG.

As can be seen from FIG. 4, although a good proportional relationship can be seen within ± 1350 Oe, if it deviates from this range, the sensor output becomes a constant value and it does not function as a sensor.

[0030]

As described above, in the optical magnetic field sensor according to the present invention, the magnetic field detecting section is composed of the detecting terminal using the RIG film as the magneto-optical material and the magnetic field adjusting member of the magnetic material. It is also possible to measure a high-intensity magnetic field that cannot be measured by the optical magnetic field sensor using the RIG film as the magneto-optical material. Further, since the RIG film is used, mass productivity can be improved and cost can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a detection unit of an optical magnetic field sensor used in an example of the present invention.

FIG. 2 is a diagram of the detection unit of FIG. 1 viewed from a light incident / emission side.

3 is a diagram showing a main part of a detection terminal of the detection unit of FIG. 1, which is composed of a PBS, a half-wave plate, an RIG film, and a PBS.

FIG. 4 is a diagram showing the results obtained in Examples 1 and 2 and a conventional example, showing the relationship between the output of the optical magnetic field sensor and the magnetic field strength.

FIG. 5 is a diagram showing a main part of a detection terminal of a detection unit used in Examples 3 and 4, and a total reflection prism, a polarizer, and a RIG.
The film, the polarizer, and the total reflection prism are arranged in this order.

FIG. 6 is a view showing the shape of a magnetic field adjusting member used in Example 5.

FIG. 7 is a view showing the shape of a magnetic field adjusting member used in Example 6.

FIG. 8 is a view showing the shape of a magnetic field adjusting member used in Example 7.

FIG. 9 is a diagram showing the shape of a magnetic field adjusting member used in Example 8.

FIG. 10 is a view showing the shape of a magnetic field adjusting member used in Example 9.

FIG. 11 is a view showing the shape of a magnetic field adjusting member used in Example 10.

FIG. 12 is a view showing the shape of a magnetic field adjusting member used in Example 11.

13 is a diagram showing the shape of a magnetic field adjusting member used in Example 12. FIG.

FIG. 14 is a view showing the shape of a magnetic field adjusting member used in Example 13.

FIG. 15 is a diagram showing the shape of a magnetic field adjusting member used in Example 14;

FIG. 16 is a diagram showing a basic configuration of a conventional optical magnetic field sensor for current measurement.

[Explanation of symbols]

1 -------- Light source 2,9 ---- Optical fiber 3,8 --- Lens 4,7 --- Polarization beam splitter 5 -------- Half wave plate 6 --- --- Magneto-optical material 10 ------ Photodetector 11 --------
Signal processing circuit 20 --- Detection unit 21,22 ---
Optical fiber 23 --- Detection terminal 24 --------
Magnetic field adjusting member 25, 26 --- PBS 27 --------
RIG film 28 ----- Half-wave plate 31,35 ---
Total reflection prism 32,34 --- Polarizer 33 --------
RIG film

Claims (8)

[Claims] 1. A method for measuring the strength of a magnetic field using rare earth iron garnet as a magneto-optical material, wherein a magnetic field adjusting member made of a magnetic material is provided in the vicinity of the rare earth iron garnet, and the substantial strength of the magnetic field applied to the rare earth iron garnet is set. , A method of measuring a magnetic field, characterized in that it is less than the saturation magnetic field strength of rare earth iron garnet. 2. The method for measuring a magnetic field according to claim 1, wherein the magneto-optical material is a rare earth iron garnet. 3. The detection terminal is covered with a magnetic field adjusting member so that a part of the detection terminal is exposed or the surface can be confirmed from the outside. Measuring method of magnetic field. 4. The method for measuring a magnetic field according to claim 1, wherein a part of the container forming the detection terminal is made of a magnetic material. 5. An optical magnetic field sensor basically composed of a light source, a magnetic field measuring detector, and an output unit, wherein the magnetic measuring detector is made of a magneto-optical material and a detection terminal and is made of a magnetic material. An optical magnetic field sensor comprising a magnetic field adjusting member. 6. The optical magnetic field sensor according to claim 5, wherein the magneto-optical material uses rare earth iron garnet. 7. The detection terminal is covered with a magnetic field adjusting member so that a part of the detection terminal is exposed or the surface can be confirmed from the outside. Optical magnetic field sensor. 8. The optical magnetic field sensor according to claim 5, wherein a part of the container forming the detection terminal is a member made of a magnetic material.